Tag Archives: ocean acidification

Notothenioid fish are typically found in the deep, cold waters of the Southern Ocean. Three species of fish native to the Ross Sea were studied to see how they may react to warmer and more acidic oceans.

To measure the effects of temperature on the fish, individuals were randomly selected and placed in one of the four experimental treatment tanks. The experimental tanks consisted of a control treatment, a low temperature and high pCO2, high temperature and low pCO2, and high temperature and high pCO2 to test the individual and overall effects of temperature and pCO2 on the three-fish species. pCO2 is the partial pressure of carbon dioxide in the water. Each fish had an acclimation period that lasted anywhere from 7 to 56 days. Measurements of fish condition and growth were recorded over the course of the experiment. A few tests were performed to analyze enzymatic changes in the liver, white muscle tissue, and gills. One of the tests, the citrate synthase activity test measured how well the fish can release stored energy.

Results

T. bernacchii, the emerald codfish, was the only fish to display any significant impact from the treatments. The growth and condition declined significantly due to temperature but slowed as the acclimation period increased. The group of fish with the faster acclimation period had the largest decline of condition and growth, especially those that also had the multi-stress (high temperature and high <em>p</em>CO2) treatment. The temperature also influenced the Emerald Codfish’s oxygen consumption and metabolic rate. The high <em>p</em>CO2 tank had a small increase in metabolic rate. There were significant increases in citrate synthase activity, the first of which occurred after 7 days in the multi-stress treatment in the gills. By the 28-day acclimation, all treatments had significantly increased in both the liver and the gills.

The bald notothen, P. borchgrevinki, metabolic rates were significantly affected by temperature in the shorter acclimation periods. Interestingly, the oxygen consumption rates decreased in the high temperature treatments over time. Time and temperature were the main drivers in the citrate synthase activity increase in the gill tissues.

Metabolic rates in T. newnesi differed significantly between the acclimation groups with temperature as the main effect. No significant difference between pCO2 and temperature was present. There was however, an increased oxygen consumption rate after the 7 and 28-day acclimation period. The T. newnesi showed the least sensitivity to the treatments. The changes in Citrate synthase activity were not statistically significant.

This group of fish, the Notothenioid fish are critical to the Ross Sea food web. The three-species studied are consumed by seals, penguins, and other top predators. Studies like this one help to predict population responses for not only the Notothenioidei suborder but also other species which depend on these individuals for food.

Temperature had a greater adverse effect on the energy demands for two of the studied species. The fish may be able to acclimate to the higher temperatures, but only to an extent. Higher temperatures may mean a decreased ability to efficiently ingest food leading to decreased growth and other detrimental effects as seen in the Emerald codfish.

It should be noted that the long-term implications of the temperature and pCO2 on growth should be cautiously interpreted due to the small sample size and lack of growth even in the control samples.

The pH of the ocean is changing incrementally, as a result of increases in atmospheric carbon dioxide. As shown in Figure 1, a proceeding decline in seawater pH has been induced by ocean acidification and will continue over the next hundred years. The ocean is expected to decline an average of 0.3 pH units by the end of the century. Changing the geochemistry of the ocean is consequently changing the biogeochemical processes of the sea, including marine microbial populations. The microbial community is extremely important to the marine carbon cycle in their role to decompose and recycle nutrients, as shown in Figure 2.

Figure 1. Predicted Ocean Surface pH Through the Year 2100.

The ocean maintains a viable level of carbon dioxide from such decomposition and subsequent respiration of organic molecules by heterotrophic bacteria. Since the industrial boom, the human obsession to industrialize is continually offsetting the balance of the ocean’s carbon dioxide levels and setting up a future of mutational distress. The burning of fossil fuels (primarily coal) and its emissions are manipulating the ocean for the worse.

Researchers Ian Joint, Scott C. Doney, and David M Karl wrote an article for the ISME Journal regarding their perspectives on the question, “Will ocean acidification affect marine microbes?”

The reasoning behind their perspective has much to do with the lack of proper research done addressing the issue of microbial function in a lowered pH oceanic environment. Much is known about calcifying organisms, such as corals and coccolithiphores, in regards to ocean acidification. With an increase in acidity, maintaining calcite and aragonite shells and skeletons becomes nearly impossible.

Most studies that are published include discussions of the ocean pH in the context of geological time scales in spatial uniformity of pH for the present-day ocean. However, pH of the oceans is not constant and there are considerable seasonal, depth, and regional variations that come into play. With that in mind, pH is naturally variable and marine organisms-particularly microbes-must already be capable of adapting to rapid and sometimes large changes in pH. Kai T. Lohbeck, Ulf Riebesell and Thortsten B. H. Reusch published an article for Nature Geoscience regarding the topic of adaptive evolution of a key phytoplankton species to ocean acidification. According to the article, they suggested that contemporary evolution could help to maintain the functionality of microbial processes at the base of marine food webs in the face of global change; that these organisms are currently facing evolutionary adaptations.

The pH levels in the ocean are not consistent, especially when considering other variables such as light, temperature, and depth. The multifactorial relationship among these variables is direct. Researchers Ian Joint, Scott C. Doney, and David M Karl presented a null hypothesis to be tested: marine microbes posses the flexibility to accommodate pH change and there will be no catastrophic changes in marine biochemical processes that are driven by phytoplankton, bacteria, and archae.

In an alternate scientific publication by J. Piontek, M. Lunau, N. Händel, C. Borchard, M. Wurst, and A. Engel, a study was conducted in regards to acidification increasing microbial polysaccharide degradation in the ocean. The ocean’s capacity for carbon dioxide storage is strongly affected by biological processes whose feedback potential is unfortunately difficult to evaluate. This article coincides with the previous considering that very little is known about potential effects ocean acidification poses not only on the microbial community themselves, but on bacterial degradation activity as a whole. Polysaccharides are a major component of organic matter, an energy source for the majority of bacterial communities. Their breakdown by bacterial enzymes seemed to have significantly accelerated during J. Piontek, M. Lunau, N. Händel, C. Borchard, M. Wurst, and A. Engel’s experimental simulation of ocean acidification. An experiment was set up to test the rate of enzymatic polysaccharide hydrolysis (how quickly bacteria could break down the macromolecule) in natural bacterioplankton communities. In this experiment, two environments were simulated: one being present day pH levels – what the ocean’s pH level is today and the latter being future day pH levels – what the ocean’s pH levels are predicted to be in the next hundred years. After each sample was incubated, concentrations of dissolved and particulate combined glucose, galactose, arabinose, and other sugars and acids were also detected. These concentrations represented the complexity of the relationships between the variables that come into play with acidification. This allowed the scientists to relate the differences in glucosidase activity (enzymes which break down glucose) and macromolecule concentration between present-day and future-ocean treatment to the increase in hydrogen ion concentration. Figure 3 illustrates the results of the above experiment with regards to an additional variable, permanent dark incubation and dark cycling incubation. The experiment revealed that the observed increase in glucosidase activity was directly proportional to the increasing acidity of the ocean water in a simulated acidification model. They also came to realize that changes in the enzymes’ activities reflected a community response of bacterioplankton to the simulated acidification as well. A collective conclusion of the experiment goes as follows: experimental results suggest that increased glucosidase activity at lowered seawater pH does not depend on the abundance of some specific bacterial strains, but reflects a community response to lowered seawater pH. This response could indicate that bacterial communities are currently undergoing adaptations to adjust to the decreasing pH. Higher enzymatic rates at lowered seawater pH are a chemical acidification effect on natural enzyme assemblages that is beneficial for the bacterial metabolism. Some might go on to further assume that come a more acidic oceanic environment, bacterioplankton communities will readily adapt and will not counter enhanced polysaccharide degradation. With a quicker degradation of polysaccharides, the bacterioplanktonic communities might flourish, quicker breakdown of sugars to be used as an energy source while simultaneously recycling nutrients back into the food web during degradation.

Figure 3. Percent loss of different macromolecules in present day oceanic pH levels and future pH levels with regards to another variable: permanent dark incubation and dark cycling incubation.

Results from different studies and perspectives show that a lot of variables must be considered when focusing on the question, “Will ocean acidification affect marine microbes?” Current analysis and comparison of freshwater pH and seawater pH is only so significant because the pH in freshwater acts on a short-term scale and the ocean acts on a far longer term. The ocean is too complex; there are too many variables to continue with the current broad-scale state of research.. Studies should go into the “micro-economics” of the ocean and its harmful relationship with acidification. There is more potential for a better understanding of a correlation between microbial communities and ocean acidification if things are broken apart and analyzed. Studying and analyzing the consequences of changes in individual variables, such as a potential threat to a major energy source of microbial communities (polysaccharides), can infer if there is in fact a present evolutionary adaptation of microbes to the increasingly acidic ocean. It’s also important to consider the possibility that microbial communities will adapt to the changes in pH but only to a certain degree before the rate of adaptation plateaus and these communities can no longer keep up with the consistent decrease in pH in the next one hundred years.

In recent years, it has become apparent that increased CO2 emissions have farther reaching consequences than simply raising the temperature of Earth’s atmosphere. A significant amount of CO2 is absorbed by the ocean, which raises its acidity through chemical reactions with water molecules. This process, termed ocean acidification, has a large number of potentially detrimental effects on biodiversity, interactions between species, and individual species fitness. Elevated CO2 levels encumber the ability of certain invertebrates, such as corals and snails, to build calcium carbonate skeletons and can drive habitat shifts that degrade ecosystems. Laboratory experiments have also shown that prolonged exposure to CO2 negatively affects the ability of fish to perform predator-avoidance behaviors.

Nagelkerken et al 2015 explores the effects of ocean acidification with in situ study, meaning the experiment was done in the natural habitat of the subject species. A field study allowed for the researchers to account for the indirect effects of changes in habitat on fish behavior and abundance, necessary to more accurately predict species responses to ocean acidification, as well as their potential consequences for ecosystems. The authors observed habitat coverage, fish habitat association, fish escape response performance, and fish and predator population density at 2 separate locations: White Island, New Zealand and Vulcano Island, Italy. Both sites are characterized by vents that naturally produce CO2, maintaining the acidity of the surrounding water at a much higher than average level, levels that the rest of the oceans may reach by the end of the century.

At both locations, habitat coverage changed significantly between the control sites (far enough away from the vents to not be affected by the elevated CO2) and the sites near the vents. Increased acidity caused ecosystem phase shifts; complex ecosystems mottled with vegetation, algae, patches of rock or sand give way to simpler communities dominated by either algae or sand near the vents. The fish species observed, the common triplefin and Bucchich’s goby, both associated primarily with algae and sand or rock bottom areas. Increased biomass of preferred habitat, along with higher levels of prey abundance in these habitats, most likely contribute to the significant difference in fish density observed between the vent and control sites. Fish density near the vents was greater than double density measured at control sites. This may have also been a result in part of the lack of predatory fish observed near the CO2 vents.

Though effects of elevated CO2 actually improved fish abundance, it still had negative effects on the behavior of the fish species. Fish at vent sites escaped threats more slowly than fish at control sites and usually waited until the threat was closer to begin moving away, indicating CO2 exposure lessened the ability of the fish to avoid predation. One exception to this, in the algae dominated habitats at the Vulcano Island site, there was little difference between the startle distance (distance from the threat to the fish when the fish starts its escape) of fish living at the control sites and fish living near the vents. Fish may begin their escape response later in this habitat because they feel more relaxed knowing they have easy access to shelter.

This study is the first example of the negative direct effects of ocean acidification on fish behavior being counteracted by indirect effects that actually increase fish abundance and survival. Contrasting laboratory-based predictions that less productive and simpler ecosystems would harm fish populations, this paper demonstrates the need for more in situ studies on the effects of elevated CO2 levels. Indirect effects, such as changes in predator and prey abundance and habitat phase-shifts, must be considered when attempting to accurately predict the consequences of climate change.

In the last decade, the concerns of how global climate change is going to affect our planet have grown. One of the main components of what is causing this climate change is the increase in carbon dioxide in our environment. There was a major increase in carbon dioxide in the atmosphere after the industrial revolution. The level of carbon dioxide in the atmosphere has risen from 280ppm to 390ppm. The carbon dioxide from the atmosphere diffuses into the ocean, which has created an increase in carbon dioxide in the ocean. With the increasing carbon dioxide levels in the ocean, the pH of the ocean will decrease leading to many detrimental effects on the animals that live there. It is predicted that by 2300 the carbon dioxide levels in the ocean will be around 1900 μAtm, which will cause the pH of the ocean to drop by 0.77. This decrease in pH will cause extreme changes in the ocean and how organisms develop and survive under these conditions is of utmost importance (Heuer, R., 2014). One of the many classes that has been studied is cephalopoda. The cephalopods include such animals as squid, cuttlefish, and octopus. They are a very important class to ocean trophic levels and to the economy and it is essential to determine what negative effects will occur to them in the coming years (Kaplan, M.B., 2013).

One of these economically important species is Doryteuthis pealeii, the longfin squid. Squid are a critical part of the food chain in the ocean because not only do they serve as prey for many organisms, such as tuna, but they also serve as predators of many organisms. In a study conducted in 2013, this certain species of squid was used. D. pealeii lives in shallow waters in coastal regions. In this study, individuals were taken from Vineyard Sound, Massachusetts on two separate occasions during their breeding seasons which lasts from May to August. The aim of this study was to calculate the difference in mantle size, statolith size, statolith characteristics, and hatching time between control embryos and embryos at an elevated carbon dioxide level of about 2200 μAtm. This is slightly above the predicted levels for the year 2300. The study found that in both trials, embryos hatched later in the carbon dioxide treatment than the control embryos. For example, in the first trial on the first day of hatching, 62.6% of embryos hatched, whereas only 0.7% of the embryos with increased carbon dioxide hatched. The negative effects of this delay may be that there is an increased chance for predation.

Picture 1: Embryo hatching times for both trials

In addition to the hatching time, there were also many other negative changes in other parts of the squid. When the mantle length was looked at between the two conditions, the mantle was significantly shorter when the squid was reared in the carbon dioxide conditions. With a shorter mantle, the squid has less ability to move. Therefore, a shorter mantle can lead to slower swim speeds and lower migration causing a smaller chance of survival. Squid also have statoliths, which are calcified structures that are critical in balance and how the animal moves in the water. Seeing as these are calcified structures, their formation is greatly related to the acid content in the water. In this study, it was found that the statoliths of the squid in carbon dioxide had decreased surface area and a greater likelihood of abnormal shape and abnormal porosity. With decreased function of the statolith, the squid cannot orient itself the correct way in the water and again has decreased survival (Kaplan, M.B., 2013). Along with this type of cephalopod, cuttlefish also show a change in an inner calcareous structure in increased carbon dioxide conditions.

Picture 2: Average statolith surface area in the control treatment vs. the carbon dioxide treatment

Some cuttlefish have a calcareous structure called a cuttlebone that is located dorsally that goes from just behind the head to the end of its body. The purpose of this bone deals with buoyancy. During the day, the chambers of the cuttlebone are filled with fluid, which make the cuttlefish able to sink, and at night this fluid is expelled, which causes the cuttlefish to stay in the same place in the water column. A study done on Sepia officinalis, the common cuttlefish, looked at morphological changes in the cuttlebone in a carbon dioxide rich environment. In this study they found that carbon dioxide exposed cuttlebones had significantly less height and length, but had a 20-55% increase in mass. The shorter height can be accounted for by the fact that the lamellae in the cuttlebone in the carbon dioxide treatment were a lot closer together, compacting the cuttlebone. In addition, the inner pillars of the cuttlebone were found to have doubled in thickness, showing a build up of carbonate and an increase in mass. A heavier cuttlebone is detrimental to a cuttlefish because in order for that structure to control buoyancy it needs to be as light as possible; the cuttlefish will not be easily able to move up the water column because it will take more work to make the animal neutrally or positively buoyant. In addition, it will be more difficult for the cuttlefish to maintain a position in the water column while hunting, which could cause starvation in the organism (Gutowska, M.A., 2010).

Average cuttlebone measurements in the control vs. carbon dioxide treatments

Research into the consequences of ocean acidification is increasingly necessary in order to determine what will happen to the ocean in the next few hundred years. The spike in the carbon dioxide content in the oceans has been directly caused my humans and it is imperative that now something is done to slow down this increase.

It’s difficult to predict the effects of near-future ocean acidification (OA) across ecoregions and ocean habitat. The body of research has been conducted under a variability of circumstances and conditions. While evidence continues to mount for OA as a global mega trend, researchers like Christopher E. Cornwall and Tyler D. Eddy call for the need to contextualize OA within local coastal communities. It is there, after all, that the combined effects of pollution, resource extraction, and preservation interact within geographically distinct units. The results of multiple stressors, anthropogenic or otherwise, can alter an ecosystem’s structure and function. In their recent study, Cornwall and Eddy suggest that management regimes rely on current global predictions as well as modeling of single-species’ response to changes in ocean chemistry.

For their study, Cornwall et al. used the intertidal and subtidal habitats from the Wellington south coast, and the Taputeranga Marine Reserve off New Zealand. Both possess similar substrate and habitat, and fall within the larger Cook Strait Region. Wellington features extant commercial and recreational fisheries that primarily target Lobster (Jasus edwardsii), Abalone (Haliotis australis and Haliotis iris), as well as Blue Cod (Parapercis colias) and Butterfish (Odax pullus). According to cited work by Breen & Kim (2006), Cornwall et al. note at the time of study that Lobster abundance had been maintained at 20% of original unfished biomass. Taputeranga Marine Reserve (MR), by contrast, was established as a no-take zone at its outset in 2008.

Building on a model developed by Eddy et al. (2014), Cornwall and Eddy describe the challenge of scaling down global predictions of OA to their study area. In the body of literature, the effects for net-calcification have been generated from a variety of “carbonate chemistry conditions.” The resulting baselines do not, on their own, serve as complete proxies that the research team could use to base their predictions on. They relied on calculating levels of “dissolved inorganic carbon and total alkalinity, pH on total scale, and partial pressure of CO2” in the survey area, and compared this to the predicted rise of CO2 concentrations between 2014 (380 ppm) and 2050 (550 ppm).

To measure the ecosystem dynamics they used Eco-modeling software EwE. They examined a fully factored set of scenarios comprised of four criteria: fished areas (Wellington), non-fished areas (MR), and the presence or absence of OA. In order to generate estimates for 2050, fishing mortality was held constant from 2008 biomass. The scenario for fished area with an absence of OA was used as the baseline of the study. To further delineate changes over time, four indicators of ecosystem interaction were synthesized:

Proportion of benthic biomass affected

Proportion of pelagic biomass affected

Impact by Trophic Level

Mean Trophic Level of community

After initial modeling, they noted that certain species showed dramatic changes in abundance across scenarios. Further sensitivity analyses, referred to as “blanket modifiers,” strengthened their assumptions about the changes in food web interaction and ecosystem function. One of the more noteworthy findings were the predictions of abundance for Lobster, a keystone species. Outside of the marine reserve Lobster numbers were maintained, albeit at a “fraction” of their original unfished biomass. In a scenario of MR + OA in 2050, however, Lobster abundance was reduced by 42%. This was due to heightened sensitivity to OA. As a result, researchers predicted there would be fewer predations on species at lower trophic levels, and subsequent shifts in the structure of the food web. In that same scenario, “Abalone, piscivorous fishes, and herbivorous fishes increased in biomass by 52%, 11%, and 13% respectively.”

These results may be counterintuitive because there is the expectation that protected areas better compensate for additional stressors than do areas under fishing exploitation. This is the case, and that was what the team correctly hypothesized. However, Cornwall et al. point out the nuances of near-future ocean acidification at a species-specific level. They maintain that the effects will be “subtle, species specific, and context dependent.” Apart from calcareous species, not all species stand to lose, and, in fact, some may flourish. Cornwall and Eddy suggest that these findings can be useful when comparing regions, and targeted catches of species, especially those that will face increased pressure from changes in ocean chemistry.

Ocean acidification is a term commonly used in the world of marine science. This process can most easily be described as the lowering of oceanic pH due to increased atmospheric carbon dioxide concentrations. However, there is much more to this complicated process, which could mean great changes for the future of our oceans.

It is no surprise that atmospheric carbon dioxide levels are increasing. Since the industrial revolution atmospheric CO2 concentrations have increased from 280 ppm to 396 ppm, and this number is expected to increase to 800 ppm by the year 2100. Unfortunately, much of this excess CO2 finds its way to the ocean, changing the natural chemistry of the water. When atmospheric CO2 is added to seawater a series of chemical reactions naturally occurs. The addition of excess CO2 shifts the equilibrium of this reaction series, resulting in increased hydrogen and lower carbonate concentrations. Because pH is equal to –log [H+] increased H+ concentrations have lowered the pH from pre-industrial 8.2 to a 7.8 (projected 2100). Carbonate is essential for calcifying organisms such as mussels, shrimp, some coral species, and more. Carbonate ions combine with calcium ions naturally found in seawater to form CaCO3, the skeletal material for many organisms. Lowered carbonate concentrations make it more difficult to form this compound, thus more difficult to calcify, and in some cases survive.